A steering device for an automobile is formed as shown in FIG. 9, transmits the rotation of a steering wheel 1 to an input shaft 3 of a steering gear unit 2, and makes front wheels have a steering angle by pushing and pulling a pair of (left and right) tie-rods 4 and 4 according to the rotation of the input shaft 3. The steering wheel 1 is supported by and fixed to a rear end portion of a steering shaft 5. While the steering shaft 5 is inserted into a cylindrical steering column 6, which is supported by a vehicle body, in an axial direction, the steering shaft 5 is rotatably supported by the steering column 6. Further, a front end portion of the steering shaft 5 is connected to a rear end portion of an intermediate shaft 8 through a universal joint 7, and a front end portion of the intermediate shaft 8 is connected to the input shaft 3 through another universal joint 9. Furthermore, an example shown in FIG. 9 is an electric power steering device that uses an electric motor 10 as a source of auxiliary power to reduce a force required to operate the steering wheel 1.
Further, as long as a front-rear direction is not otherwise described, the front-rear direction means a front-rear direction of a vehicle in the entirety of this specification and claims.
FIGS. 10 and 11 show a structure disclosed in Patent Document 1 as an example of a more specific structure of the electric power steering device. An inner column 11 and an outer column 12 are combined with each other so that a total length of the inner column 11 and the outer column 12 can be reduced at the time of secondary collision. As a result, a steering column 6a is formed. The steering column 6a is supported by the vehicle body. Further, a lower shaft 13 and an upper shaft 14 are combined with each other so that torque can be transmitted between the lower and upper shafts 13 and 14 and a total length of the lower and upper shafts 13 and 14 can be reduced at the time of secondary collision. As a result, a steering shaft 5a, which is rotatably supported in the steering column 6a, is formed. A steering wheel 1 (see FIG. 9) is fixed to a rear end portion of the upper shaft 14 that protrudes from a rear end opening of the outer column 12. Furthermore, a housing 15 is joined and fixed to a front end portion of the inner column 11, and a front half portion of the lower shaft 13 is inserted into the housing 15. The housing 15 includes a stepped cylindrical housing body 16 that is joined and fixed to the front end portion of the inner column 11, and a substantially annular lid body 17 that is fixed to a front end portion of the housing body 16.
The lower shaft 13 as an input shaft and an output shaft 19, which are coaxially connected to each other by a torsion bar 18, are rotatably supported in the housing 15. Most of the torsion bar 18 except for a front end portion thereof is disposed on the inner diameter side of the lower shaft 13 that is formed in the shape of a hollow shaft. Moreover, the output shaft 19 is disposed on the front side of the lower shaft 13, and is supported by a pair of ball bearings 20 and 21 so as to be rotatable relative to the housing 15. More specifically, an intermediate portion of the output shaft 19 is rotatably supported by the ball bearing 20 that is fitted and fixed to an inner peripheral surface of the lid body 17, and a rear end portion of the output shaft 19 is rotatably supported by the ball bearing 21 that is fitted and fixed into a first cylindrical surface portion 22 that is formed at a front end portion (which corresponds to one end portion in the axial direction) of the inner peripheral surface of the housing body 16. Further, a worm wheel 23 is fitted around and fixed to a rear end portion of the output shaft 19. A worm 24, which is rotatably supported in the housing 15, meshes with the worm wheel 23. Furthermore, the electric motor 10 (see FIG. 9) is supported by and fixed to the housing 15, and an output shaft of the electric motor 10 is joined to a base end portion of the worm 24 so that torque can be transmitted to the base end portion of the worm 24.
Moreover, a cylindrical portion 26, which includes a female stopper portion 25 having an uneven shape in a circumferential direction and formed on an inner peripheral surface thereof, is formed at the rear end portion of the output shaft 19. Meanwhile, a male stopper portion 27, which has an uneven shape in the circumferential direction and of which the outer diameter (the diameter of a circumcircle) is smaller than the outer diameter of the front end portion, is formed on the front end portion of the outer peripheral surface of the lower shaft 13. The male stopper portion 27 and the female stopper portion 25 are engaged with each other so as to be relatively rotatable within a predetermined angular range (a range of, for example, ±5° from a neutral state where the torsion bar 18 is not twisted). Accordingly, the excessive torsion of the torsion bar 18 is prevented.
Further, the lower shaft 13 is made of steel, which is magnetic metal, and a torque detecting uneven portion 28, which has an uneven shape in the circumferential direction, is formed at the front end portion of the outer peripheral surface of the lower shaft 13. A cylindrical torque detecting sleeve 29 made of non-magnetic metal having conductivity, such as an aluminum alloy, is disposed on the outer diameter side of the torque detecting uneven portion 28. A base end portion of the torque detecting sleeve 29 is fitted around and fixed to the cylindrical portion 26. Furthermore, a plurality of window holes 30 and 30 are formed at a portion, which is positioned on the outer diameter side of the torque detecting uneven portion 28, of the torque detecting sleeve 29. Moreover, a torque detecting coil unit 31, which is fitted and fixed into the housing 15 (the housing body 16), is disposed on the outer diameter side of the torque detecting uneven portion 28 and the torque detecting sleeve 29.
The torque detecting coil unit 31 is fitted and fixed into a second cylindrical surface portion 32 that is formed on a portion, which is positioned on the rear side (which corresponds to the other side in the axial direction) of the first cylindrical surface portion 22, of the inner peripheral surface of the housing body 16. The torque detecting coil unit 31 includes a cylindrical detection body 33, a pedestal 34 that is formed so as to protrude outward from the outer peripheral surface of the detection body 33 in a radial direction, and a connection terminal 36 that includes a plurality of pins 35 and 35 embedded into the pedestal 34. The detection body 33 includes a plurality of (two in the example shown in the drawings) cylindrical coil bobbins 37 and 37 that are formed by a winding of coils, and a yoke member 38 that covers the respective coil bobbins 37 and 37. The connection terminal 36 is formed so as to protrude outward from a part of a circumference of the detection body 33 in the racial direction, and is connected to the respective coil bobbins 37 and 37. Meanwhile, the second cylindrical surface portion 32 is formed concentrically with the first cylindrical surface portion 22, and has a diameter smaller than a diameter of the first cylindrical surface portion 22. For this reason, the torque detecting coil unit 31 (the detection body 33), which is fitted and fixed into the second cylindrical surface portion 32, is disposed concentrically with the ball bearing 21 fitted and fixed into the first cylindrical surface portion 22, and the outer diameter of the torque detecting coil unit 31 is smaller than the outer diameter of the ball bearing 21.
The connection terminal 36 is connected to a circuit board 40 through a connection hole 39 that is a through hole formed at a portion matching the second cylindrical surface portion 32 in the front-rear direction on a part of the housing body 16 in the circumferential direction. The circuit board 40 is disposed in a storage space 41 that is formed at a portion, which matches the connection hole 39 in the circumferential direction, of the outer peripheral surface of the housing body 16 so as to be recessed inward in the radial direction. The storage space 41 is closed from the outside by a lid member 42 that is mounted on an outer peripheral surface of the housing body 16. Further, a recessed groove 43, which is recessed outward in the radial direction to allow the connection terminal 36 to pass therethrough in the front-rear direction during assembly work, is formed at a portion, of which a phase corresponds to a phase of the connection hole 39 in the circumferential direction, of the inner peripheral surface of the housing body 16 between the connection hole 39 and the first cylindrical surface portion 22 in the front-rear direction.
When torque as a steering force is applied to the steering shaft 5a by the driver's operation of the steering wheel 1 in the case of the electric power steering device having the above-mentioned structure, the torsion bar 18 is elastically twisted (within a predetermined angular range) so as to correspond to a direction and a magnitude of this torque. Accordingly, a change of impedance occurs on the coil bobbins 37 and 37 of the torque detecting coil unit 31 due to the change of a positional relationship between the torque detecting uneven portion 28 and the torque detecting sleeve 29 in the circumferential direction. For this reason, it is possible to detect the direction and the magnitude of torque on the basis of the change of impedance. The electric motor 10 generates auxiliary power corresponding to a torque detection result. The auxiliary power is applied to the output shaft 19 after being increased by a worm-type speed reducer 44 that includes the worm 24 and the worm wheel 23 meshing with each other. As a result, a force, which is required for a driver to operate the steering wheel 1, is reduced.
Meanwhile, when the torsion of the torsion bar 18 reaches an upper limit on one side or the other side of the predetermined angular range due to the input of large torque to the steering shaft 5a from the steering wheel 1, the female stopper portion 25 and the male stopper portion 27 mesh with each other in the circumferential direction. Further, a part of torque is directly transmitted to the output shaft 19 from the lower shaft 13 on the basis of the mesh.
Incidentally, when the electric power steering device having an above-mentioned structure is assembled, there is a possibility that following problems may occur during work for fitting and fixing the torque detecting coil unit 31 into the second cylindrical surface portion 32 formed on the inner peripheral surface of the housing body 16.
In recent years, an importance of a reduction of a size or weight of the electric power steering device has increased in order to further improve a fuel saving of an automobile. For this reason, it is considered that the size or weight of the output shaft 19 of the torque measuring unit or peripheral components thereof needs to be reduced. It is possible to reduce the diameters of the output shaft 19 and the ball bearings 20 and 21 among the output shaft and the peripheral components while ensuring torque detection performance. However, sufficient height of a terminal is necessary for a connection of the connection terminal 36 to the circuit board 40. Meanwhile, work for fitting and fixing the torque detecting coil unit 31 into the second cylindrical surface portion 32 has been performed in the past such that the torque detecting coil unit 31 is inserted into the housing body 16 from an opening portion close to a front end of the housing body 16 (close to the first cylindrical surface portion 22) while a central axis O31 of the torque detecting coil unit 31 and a central axis O16 of the housing body 16 correspond to each other as shown in FIGS. 12 and 13. For this reason, when a distance (H) between a center of the torque detecting coil unit 31 (the detection body 33) and an end edge of the connection terminal 36 is larger than a half (d) of an inner diameter of the first cylindrical surface portion 22 (H>d), the connection terminal 36 interferes with the housing body 16. Accordingly, assembly work cannot be performed.
Meanwhile, obliquely inserting the torque detecting coil unit 31 into the housing body 16 is also considered to solve these problems. However, in this case, there is a new problem in that it is also difficult to perform automatic assembly due to a deterioration of workability.